crosses between genetically modified (gm) oilseed rape and a wild relative produce hybrid plants that are as toxic to insects as the original crop. Though it is still unclear how such hybrids fare in the wild, the finding is likely to be seized on by environmentalists as proof that field trails of gm crops are unsafe.

During laboratory experiments, Matthew Halfhill at the Greensboro-based University of North Carolina and colleagues took oilseed rape (canola) modified to contain the insect-resistance gene Bt and crossed it with a related weed, birdseed rape (Brassica rapa). They made 11 crosses using different combinations of plant lines. Five of them produced stable hybrids containing the Bt gene. These expressed insecticide produced by the gene at levels similar to the gm parent and were highly toxic to insects.

The finding will fuel fears that